Formation of Ga_2O_3 barrier layer in Cu(InGa)Se_2 superstrate devices with ZnO buffer layer

摘要

The junction formation when Cu(InGa)Se_2 is deposited onto ZnO in a superstrate configuration (glass/window/buffer/Cu(InGa)Se_2/contact) is investigated by x-ray photoelectron spectroscopy and analysis of device behavior. When Cu(InGa)Se_2 is deposited on ZnO, a Ga_2O_3 layer is formed at the interface. Approaches to avoid the formation of this unfavorable interlayer are investigated. This includes modifications of the process to reduce the thermal load during deposition and improvement of the thermal stability of the ZnO buffer layer. It was demonstrated that both lowering of the substrate deposition temperature and deposition of the ZnO buffer layer at elevated temperature limits the Ga_2O_3 formation. The presence of Ga_2O_3 at the junction does affect the device behavior, resulting in a kink in JV curves measured under illumination. This behavior is absent in devices with limited Ga_2O_3 formation.